1. Field of the Invention
The present invention relates to the field of impact responsive actuating apparatus; more particularly, it relates to such apparatus in missiles having impact discrimination to prevent unintended detonation or fusing.
2. Description of the Prior Art
A problem with explosive missiles, such as rockets and re-entry vehicles, mortar or artillery shells, is unintended and premature detonation which may cause injury to friendly troops and objects. Such premature detonation may be caused by pre-launch damage to the missile, by launching stresses, or by the missile impacting an intervening object before reaching the target.
Premature detonation problems associated with pre-launch damage and launching stresses are normally solved by maintaining the missile in an unarmed condition until after the launch has been completed. White, et al. (U.S. Pat. No. 3,750,583) and Furlani, et al. (U.S. Pat. No. 3,653,324), for example, disclose arming apparatus. Launch accelerations perform the arming in the apparatus of White, et al. The apparatus of Furlani, et al, additionally examines the "launch signatures", that is, the various launch stresses, and arms the missile only if all of such "signatures" fall within predetermined limits. Missiles upon which such or similar apparatus are installed are not armed until they have been properly launched. Danger of premature detonation caused by pre-launch damage and launch stresses is thereby minimized.
Assuming, however, that a missile is provided with an appropriate arming apparatus, a substantial problem still exists relative to premature detonation caused by the missile impacting intervening objects before reaching the intended target. Such intervening objects may include tree branches, leaves, undergrowth, raindrops, airborne ice crystals and airborne materials such as sand and debris from prior explosions.
If the intended target is very hard, like concrete, steel or hard earth, an impact fuse or detonator responsive only to a high impact force may be used to prevent premature detonation caused by lesser impacts with the types of intervening objects mentioned above. However, if the intended target is itself comparatively soft, such as swampy ground or water, impact discrimination is less easily accomplished; if too hard an impact is required for detonation, in an attempt to provide impact discrimination, detonation may not occur when the target is hit.
Zimmerman (U.S. Pat. No. 3,786,758) and Cummings (U.S. Pat. No. 3,805,703) disclose apparatus for discriminating between impact with the intended target and impact with intervening objects. Zimmerman discloses a plurality of series connected impact sensors or "switches" positioned around the outside of the missile nose. Detonation of the missile occurs only when all switches are simultaneously activated, it being assumed that intervening objects (specifically raindrops in the disclosure) will be randomly distributed so that all of the switches will not be impacted at the same time until the target itself is impacted. However, an inordinately large number of sensors is required to insure that all will not be simultaneously impacted under very heavy rain conditions. This adds to system complexity and cost, and introduces reliability problems.
Cummings discloses an electronic integrating comparator which detonates the missile only when the impact time duration exceeds a predetermined time duration. It was noted that the impact time for tree branches and other material, referred to collectively as "canopy", is comparatively short compared to that of impact with a hard target (before the sensors are impact damaged). If, however, comparatively unyielding obstacles, such as large tree limbs, are impacted, the predetermined impact duration may be exceeded and premature detonation may result.
Fohrmann, et al. (U.S. Pat. No. 3,440,961) and Bliss (U.S. Pat. No. 3,158,705) disclose plural impact sensors connected in parallel to insure missile detonation upon impact with any of the sensors, rather than to provide impact discrimination.
For the reasons set forth above, and others, additional improvements in the field of impact discrimination are still required.